From 0c73259f7f67af145d23ced823739fe6cdc11835 Mon Sep 17 00:00:00 2001
From: abdoulrasheed <abdulrasheedibrahim47@gmail.com>
Date: Fri, 17 Jul 2026 19:00:09 +0100
Subject: [PATCH] gh-153855: Fix BasicInterpolation crash on None-valued
 interpolation reference

---
 Lib/configparser.py                                   |  4 ++++
 Lib/test/test_configparser.py                         | 11 +++++++++++
 .../2026-07-17-18-53-45.gh-issue-153855.h6YZOX.rst    |  1 +
 3 files changed, 16 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-07-17-18-53-45.gh-issue-153855.h6YZOX.rst

diff --git a/Lib/configparser.py b/Lib/configparser.py
index 3c452afe8ade485..5cfc21b4d663d64 100644
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -471,6 +471,10 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
                 except KeyError:
                     raise InterpolationMissingOptionError(
                         option, section, rawval, var) from None
+
+                if v is None:
+                    continue
+
                 if "%" in v:
                     self._interpolate_some(parser, option, accum, v,
                                            section, map, depth + 1)
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index 4783943f71a1092..9133d8fc43f200c 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -1379,6 +1379,17 @@ class RawConfigParserNoValueAndExtendedInterpolationTest(
 ):
     config_class = configparser.RawConfigParser
 
+class BasicInterpolationWithAllowNoValueTest(unittest.TestCase):
+    def test_interpolation_with_allow_no_value(self):
+        cf = configparser.ConfigParser(allow_no_value=True)
+        cf.read_string(textwrap.dedent("""
+            [s]
+            a
+            b = x%(a)sy
+        """))
+        self.assertIsNone(cf["s"]["a"])
+        self.assertEqual(cf.get("s", "b"), "xy")
+
 
 class ConfigParserTestCaseTrickyFile(CfgParserTestCaseClass, unittest.TestCase):
     config_class = configparser.ConfigParser
diff --git a/Misc/NEWS.d/next/Library/2026-07-17-18-53-45.gh-issue-153855.h6YZOX.rst b/Misc/NEWS.d/next/Library/2026-07-17-18-53-45.gh-issue-153855.h6YZOX.rst
new file mode 100644
index 000000000000000..64d16508ebed00c
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-07-17-18-53-45.gh-issue-153855.h6YZOX.rst
@@ -0,0 +1 @@
+Fix :class:`configparser.BasicInterpolation` raising ``TypeError`` when interpolating a reference to a value-less option with ``allow_no_value=True``; it now treats the missing value as empty, like :class:`configparser.ExtendedInterpolation`.